This invention relates generally to material handling vehicles and, more particularly, to an improved apparatus for controlling a sideshift carriage in such vehicles which are particularly adapted for narrow aisle use.
The high cost of warehouse space makes it economically desirable to extend storage racks vertically and also to provide the narrowest possible aisles between adjacent storage racks. Minimum aisle width is ordinarily dictated by the material handling vehicle to be used in the aisle as well as the size of the material to be stored. Material is typically stored in pallet sized loads and, hence, a desired pallet size is selected for use in a given warehouse.
In an attempt to reduce aisle size, side loading trucks have oftentimes replaced standard fork trucks since fork trucks must turn 90.degree. to face a rack in order to pick up or deposit a load. Even fork trucks designed to have minimum turning radii thus require relatively large aisle widths.
Side loading trucks, on the other hand, travel longitudinally along an aisle and are provided with a load shifting mechanism which allows a load to be extended laterally beyond one or, more often, both sides of the truck and be lowered onto or picked up from a shelf of a storage rack. Such side loading trucks ordinarily utilize a laterally shiftable traverse carriage having a load supporting or manipulating device, typically a pair of load forks, pivotally mounted to the traverse carriage such that it can be rotated through 180.degree. about a vertical axis to access each side of an aisle.
Since a side load truck need not turn to pick up or deposit a load, the aisle width required barely exceeds the truck width. Some designs of side load trucks utilize a laterally fixed elevatable carriage which in turn supports a laterally moveable fork carriage. The fixed carriage width obviously must be less than the aisle width to afford adequate clearance for the truck to move up and down the aisles. This limitation reduces the overall lateral shifting of the fork carriage or traverse carriage which in turn limits the distance that the forks can be extended into a storage rack to deposit or pick up a load.
Such limited extension of the load supporting device (typically forks) into a rack can lead to a multiple step procedure for storing or retrieving a load from a shelf of a storage rack. Hence, a load or pallet being stored has to be extended as far as possible into the rack by the limited motion of the traverse carriage, then be set down on the rack with the traverse carriage being partially retracted and then again being raised to pick up the load and position it more completely into the rack. Such multiple step operation may considerably slow down material handling.
To overcome such multiple step operation, an intermediate carriage is positioned between the laterally fixed elevatable carriage and the traverse carriage. The traverse carriage may then be driven to one end of the intermediate or sideshift carriage and then the intermediate carriage itself may be sideshifted in the same direction to extend the forks and load further into a storage rack. Thus, the distance which a load may be laterally shifted is the sum of the distance which the intermediate carriage is shifted and the distance which the traverse carriage is shifted.
The lateral motions of the traverse carriage and the intermediate or sideshift carriage are typically controlled independently of each other by separate controls activated by the operator of the truck. In any event, the operator after having positioned a load onto the forks must move the load to a position approximately centered relative to the truck so that the load may be repositioned on another shelf of a storage rack, removed for shipment or moved to some other desired location.
While the operator in some side loader trucks is elevated to provide a better view of the load manipulation, the operator still must position the traverse carriage and the intermediate sideshift carriage manually. Errors in positioning a load can result in either the load or the fork supporting mechanism extending excessively beyond one or the other side of the truck resulting in collisions with either portions of the storage racks or other goods stored on the racks as the truck moves along an aisle.
It is, thus, apparent that the need exists for an improved control system to permit the operator of a material handling vehicle to more accurately position a load at a preferred load carrying position prior to movement of the truck.